1. Field of the Invention
The present invention relates to isolated polypeptides having alpha-glucuronidase activity and isolated polynucleotides encoding the polypeptides. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides.
2. Description of the Related Art
Plant cell wall polysaccharides constitute 90% of the plant cell wall and can be divided into three groups: cellulose, hemicellulose, and pectin. Cellulose represents the major constituent of call wall polysaccharides. Hemicelluloses are the second most abundant constituent of plant cell walls. The major hemicellulose polymer is xylan. The structure of xylans found in cell walls of plants can differ significantly depending on their origin, but they always contain a beta-1,4-linked D-xylose backbone. The beta-1,4-linked D-xylose backbone can be substituted by various side groups, such as L-arabinosyl, D-galactosyl, acetyl, feruloyl, p-coumaroyl, and glucuronyl residues.
The biodegradation of xylan-containing material depends on two classes of enzymes: endoxylanases and beta-xylosidases that degrade the xylan backbone. Endoxylanases (EC 3.2.1.8) cleave the xylan backbone into smaller oligosaccharides, which can be further degraded to xylose by beta-xylosidases (EC 3.2.1.37). Biodegradation of xylan-containing material also requires accessory enzyme activities that remove non-xylose substituents, e.g., glucuronic acid substituents, from the xylan backbone. Such accessory enzyme activities include, for example, acetylxylan esterase, arabinase, alpha-glucuronidase, ferulic acid esterase, and p-coumaric acid esterase.
Alpha-glucuronidases are produced naturally by several microorganisms including Trichoderma reesei RutC30 (Siika-aho et al., 1994, Enzyme Microb. Technol. 16: 813-819), Trichoderma viride (Ishihara et al., 1990, Bull. For. & For. Prod. Res. Inst. 359: 141-157), Aspergillus niger (Uchida et al., 1992, Biosci. Biotech. Biochem. 56: 1608-1615), Thermoascus aurantiacus (Khandke et al., 1989, Arch. Biochem. Biophys. 274: 511-517), and Thermoanaerobacterium sp. strain JW/SL-YS485 (Shao et al., 1995, Appl. Environ. Microbiol. 61: 1077-1081). WO 1997/043423 discloses alpha-glucuronidases from Aspergillus. 
Several reports have shown a synergistic effect between xylanase, beta-xylosidase and alpha-glucuronidase in the breakdown of glucuronoarabinoxylans (Siika-aho et al., 1994, supra). Alpha-glucuronidase therefore has application in the total hydrolysis of hemicellulose to produce xylose (Uchida et al., 1992, J. Ferment. Bioeng. 74: 153-158).
The present invention relates to polypeptides having alpha-glucuronidase activity and polynucleotides encoding the polypeptides.